Synthesis and evaluation of basic oxygen furnace slag based geopolymers for removal of metals and sulphates from acidic industrial effluent-column study

Abstract:Basic Oxygen furnace slag (BOFS) based geopolymers with open porosity ranging from 21%–57 % and density between 1255 kg/m3-2432 kg/m3 were synthesized. The synthesized geopolymers potential; to be used as attenuators for metal removal and neutralization of Acid Mine Drainage (AMD); were assessed and evaluated through column test studies conducted over a period of 133 days. The results show that BOFS based geopolymer composites can be used as attenuators as over 99 % metals were removed during the first 50 days. The results also revealed that higher porosity promoted greater neutralizing ability by dissolution of soluble salts from the BOFS based geopolymer; which improves the removal efficiencies of sulphates, metals and neutralization of AMD. Characterization of the composites after contact with AMD revealed that gypsum was the main mineral phase in the geopolymers indicating that precipitation was the major mechanism that enhanced metal and sulphates removal. BOFS based geopolymers can be used to replace armoring neutralizing agents such as limestone. The research contributes to sustainable development by addressing the environmental pollution posed by AMD and utilization of BOFS as a medium for remediation of AMD. The utilization of BOFS for remediation of AMD mitigates and responds to the environmental problems and demands associated with such waste

Fixed bed column studies for decontamination of acidic mineral effluent using porous fly ash-basic oxygen furnace slag based geopolymers

Abstract: This paper presents column studies conducted to evaluate and assess the potential use of Fly Ash (FA). Basic Oxygen Furnace Slag (BOFS) based geopolymers to remove metals, sulphates and acidity from Acid Mine Drainage (AMD). Geopolymers were prepared using NaOH, Fly ash (FA) was used as source of silica additive to supplement BOFS. The blending ratio was fixed to 10% FA and the S/L ratio was kept 20%. The H2O2 was used as a blowing agent to increase the porosity of the FA/BOFS based geopolymer at four different percentages (1.5%, 1%, 0.5% and 0%). The four different geopolymers with distinct porosities were employed in different columns respectively. It was found that over 99% removal efficiency of metals and sulphates was achieved in the first 60 days of column studies. The dissolution of Ca(OH)2 was the main constituent responsible for the removal of acidity in AMD. Characterization revealed that precipitation was the main mechanism for removal of metals. Gypsum was the main byproduct formed with precipitated metals presented by goethite, spertite and manganite

Development of lightweight construction blocks by alkaline activation of BOF slag

Abstract: Large quantities of basic oxygen furnace (BOFS) are dumped in landfills of which the available land for land-filling of large quantities of waste is reducing all over the world. It is therefore im-portant to develop processes which beneficiates solid waste; BOF slag specifically. The present study attempts to investigate the potential to synthesize BOF slag based light weight construc-tion blocks. The effects of several factors on the UCS of BOF slag based light weight construc-tion blocks (LWCB) was also investigated. The test variables were molarities of sodium hydrox-ide (NaOH) (5 M, 10 M and 15 M); the solid to liquid ratio (20 %, 25 % and 30 %); the sodium silicate (Na2SiO3) to Na! OH ratio (0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 and 3:1); the curing temperature (40°C, 80°C and 100°C). It was found that optimum synthesis conditions were 5M NaOH, 80°C and 1:1 Sodium Silicate: NaOH ratio. The LWCB composite met the minimum requirements for ASTM C34-13, C129-14a and South African standard (SANS227: 2007)

The removal of Ni & Cu from a mixed metal system using sodium borohydride as a reducing agent

Abstract: Removal of nickel (II) and copper (II) from aqueous solutions using NaBH4 as a reducing agent was studied. Reduction crystallization was achieved in a batch reactor at 65oC using seeded experiments. The effect of using different molar ratios of [Ni2+]:[BH4-] namely; 1:1, 1:0.25 and 1:0.1 and seeding materials on the rate of reduction was also investigated. The results obtained showed that NaBH4 is an effective reducing agent for the removal of Ni2+ and Cu2+ from effluents. Using a molar ratio of 1:0.1 of [Ni2+]:[BH4-] and Fe and Ni as a seeding material over 99% metal removal was achieved. Ni as a seeding material yielded the best results as it is autocatalytic although there was no significant difference in the rate of reduction compared to that obtained when Fe was used as a seeding material

The Removal of Cu (II) from aqueous solution using sodium borohydride as a reducing agent

Abstract: The removal and recovery of metals from wastewater has been a subject of significant importance due the negative impact these toxic metals have on human health and the environment as a result of water and soil pollution. Increased use of the metals and chemicals in the process industries has resulted in generation of large quantity of effluents that contains high level of toxic metals and other pollutants. The objective of this work was to recover of Cu in its elemental form as metallic powder from aqueous solution using NaBH4 as a reducing agent. Reductive precipitation was achieved in a batch reactor at 65oC using Cu powder as a seeding material. This study also investigated the effect of concentration of sodium borohydride (NaBH4) as a reducing agent. The amount of NaBH4 was varied based on mole ratios which are 1:1, 1:0.25 and 1:0.1 to recover Cu from synthetic wastewater. The results obtained showed that sodium borohydride is an effective reducing agent to recover Cu from wastewater. The optimum concentration of NaBH4 that gives the best results the 1:1 molar ratio with over 99% Cu removal

Remesas de alimentos transfronterizas y transferencias móviles: Las experiencias de los migrantes zimbabuenses en Ciudad del Cabo, Sudáfrica

Mobile transfers have become a defining feature of cross-border remittance transmission in Sub-Saharan Africa (SSA). However, recent studies on mobile transfers have mainly focused on cash remittances and need to pay more attention to mobile food transfers. This paper addresses this research gap on mobile food transfers by examining cross-border food remittances and mobile transfers by Zimbabwean migrants residing in Cape Town, South Africa, to their families and friends back home. In this paper, we seek to understand the factors influencing the uptake of digital food remittances by Zimbabwean migrants who have lived in South Africa for at least three years. The paper is based on a mixed research study carried out in Cape Town during the nationwide COVID-19 lockdown in 2020. The mixed-methods study involved a questionnaire survey of 100 Zimbabwean nationals that was complemented by in-depth interviews with 10 participants selected from the interviewed group. The study findings reveal that the national COVID-19 pandemic lockdown disrupted informal food-remitting channels and, at the same time, helped to solidify the digital and mobile food transfers across national borders that have emerged in SSA in recent years.Las transferencias móviles se han convertido en un rasgo definitorio de la transmisión transfronteriza de remesas en el África subsahariana (ASS). Sin embargo, los estudios recientes sobre las transferencias móviles se han centrado principalmente en las remesas en efectivo y es necesario prestar más atención a las transferencias móviles de alimentos. Este artículo aborda esta laguna en la investigación sobre las transferencias móviles de alimentos examinando las remesas transfronterizas de alimentos y las transferencias móviles de los emigrantes zimbabuenses que residen en Ciudad del Cabo (Sudáfrica) a sus familias y amigos en su país. En este trabajo, tratamos de entender los factores que influyen en la aceptación de las remesas digitales de alimentos por parte de los emigrantes zimbabuenses que han vivido en Sudáfrica durante al menos tres años. El artículo se basa en un estudio de investigación mixto realizado en Ciudad del Cabo durante el cierre nacional de COVID-19 en 2020. El estudio de métodos mixtos incluyó una encuesta por cuestionario a 100 ciudadanos de Zimbabue que se complementó con entrevistas en profundidad a 10 participantes seleccionados del grupo entrevistado. Las conclusiones del estudio revelan que el bloqueo nacional por la pandemia COVID-19 interrumpió los canales informales de transmisión de alimentos y, al mismo tiempo, contribuyó a consolidar las transferencias digitales y móviles de alimentos a través de las fronteras nacionales que han surgido en el ASS en los últimos años

The Mae I assay for scoring atrazine resistance is codon-usage dependent in legumes

A research experiment on herbicide atrazine usages as observed out in Zimbabwe.Nine different cowpea varieties were grown and total deoxyribonucleic acid (DNA) isolated from the young leaves. This DNA was used to amplify a 291 base pair fragment that contained codon 264 of the psb A gene. The primers used were designed based on the soybean psb A gene sequence. The 291 base pair fragment was digested with the restriction enzyme Mae I to assay for sensitivity/resistance to atrazine using a published method. When Mae I did not cut the 291 base fragment, the whole gene was amplified by the polymerase chain reaction, cloned into pBSK+ll (Stratagene, CA, USA) and sequenced around codon 264. Codons 263 and 264 were found to be GCA and AGT respectively. UWGCG and BLASTsearchesofthepsbAgenesequences in the databases confirmed that Mae I has a recognition site that overlaps with codons 263 and 264 in some legumes but not in others. The Mae I assay used by Cheung and co-workers is therefore not universal but depends on codon usage in legumes

Mechanical properties and structure of Fly ash modified Basic Oxygen Furnace Slag based geopolymer masonry blocks

Abstract: The objective of this research was to investigate the effect of Fly ash as a source of Si and Na on the mechanical performance of the Basic Oxygen Furnace Slag based (BOFS) geopolymer. BOFS has the lowest SiO2, Al2O3, Na2O content compared to other aluminosilicate sources (fly ash, metakaolin, granulated blast furnace slag and mine tailings); which have been used to effectively in geopolymer synthesis. SiO2 and Al2O3, contents of BOFS are respectively 5-7 times and 6-8 times lower than those of fly ash, metakaolin and granulated furnace slag (GBFS). This study evaluated the potential use of fly ash as a source of Si and Al to improve the mechanical performance of a BOFS based geopolymer. The influence of varying amount of Coal Fly Ash (FA) (10–50%) on UCS was studied. The effects of several factors on the UCS of BOFS geopolymer were also investigated. The test variables were molarities of sodium hydroxide (NaOH) (5 M, 10 M and 15 M); the solid to liquid ratio (20 %, 25 % and 30 %); and the curing temperature (20°C, 40°C, 80°C and 100°C). It was established that most favorable conditions for the geopolymer synthesis were FA was 10% of the mixture, 5M NaOH and 80°C curing temperature. Attempts has been made to relate the microstructure of BOFS/FA based composite with properties of geopolymer. Aggregation was identified as the main particulate process as established by the evolution of the particle size distribution (PSD) and its derived moments during the geopolymerisation process. The morphology of the particles appeared flaky and fluffy. The developed composite met the minimum requirement of ASTM C34-13 for a structural clay load bearing non exposed masonry and load bearing exposed side construction masonry

Comparison of Two Methods for Noninvasive Determination of Stroke Volume During Orthostatic Challenge

Background: The real time, beat-by-beat, non-invasive determination of stroke volume (SV) is an important parameter in many aerospace related physiologic protocols. In this study, we compared simultaneous estimates of SV calculated from peripheral pulse waveforms with a more conventional non-invasive technique. Methods: Using a prospective, randomized blinded protocol, ten males and nine females completed 12-mm tilt table protocols. The relative change (%(Delta)) in beat-to-beat SV was estimated non-invasively from changes in pulse waveforms measured by application of infrared finger photoplethysmography (IFP) with a Portapres(Registered TradeMark) blood pressure monitoring device and by thoracic impedance cardiography (TIC). The %(Delta) SV values were calculated from continuous SV measurements in the supine posture and over the first 10 s (T1), second 10 s (T2), and 3.5 minutes (T3) of 80deg head-up tilt (HUT). Results: The average %(Delta) SV measured by IFP at T1 (-11.7 +/- 3.7 %) was statistically less (P or = 0.322) than the average %(Delta) SV measured by TIC at T2 (-21.8 +/- 2.5 %), and T3 (-22.6 +/- 2.9 %). Correlation coefficients (r(sup 2)) between IFP and TIC were 0.117 (T1), 0.387 (T2), and 0.7 18 (T3). Conclusion: IFP provides beat-to-beat (real time) assessment of %(Delta) SV after 20 sec of transition to an orthostatic challenge that is comparable to the commonly accepted TIC. Our data support the notion that IFP technology which has flown during space missions can be used to accurately assess physiological status and countermeasure effectiveness for orth static problems that may arise in astronauts after space flight. While the peripherally measured IFP response is slightly delayed, the ease of implementing this monitor in the field is advantageous